1. Field of the Invention
The present invention relates to a light emitting polymer and an organic light emitting device, and more particularly to a light emitting polymer including a phosphorescence unit and a fluorescence unit, and an organic light emitting device including the light emitting polymer.
2. Description of the Related Art
Organic light emitting devices which include a pair of electrodes and an organic layer interposed between the electrodes are self-emission displays that emit light due to the recombination of electrons and holes in the organic layer when a current is applied to the electrodes. The organic light emitting devices have advantages such as being lightweight, and having simple constitutional elements, a simple fabrication process, a superior image quality, and a wide viewing angle. Furthermore, the organic light emitting devices can display high quality dynamic images and have high color purity, and also have electrical properties suitable for use in portable electronic equipment such as low power consumption and low driving voltage.
Generally, organic light emitting devices include: an anode on a substrate; a hole transport layer, an emissive layer, an electron transport layer, etc. as organic layers on the anode; and a cathode on the organic layers.
When a current is applied between the anode and the cathode, holes injected from the anode are transported to the emissive layer through the hole transport layer, and electrons injected from the cathode are transported to the emissive layer through the electron transport layer. The transported holes and electrons recombine in the emissive layer to form excitons. A radiative decay of the excitons is induced to emit light having a wavelength corresponding to a band gap of the excitons.
Compounds that are used to form an emissive layer of an organic light emitting device are classified into a fluorescent compound using singlet excitons and a phosphorescent compound using triplet excitons according to light emitting mechanisms. The emissive layer can be formed using a fluorescent compound or a phosphorescent compound, or by doping the fluorescent compound or the phosphorescent compound on an appropriate host. When the emissive layer is formed using the fluorescent or phosphorescent compounds with the host, singlet excitons and triplet excitons are formed on the host as a result of electron excitation. The ratio of the singlet excitons to the triplet excitons is 1:3.
When a fluorescent compound is used to form an emissive layer in an organic light emitting device, it has the disadvantage that triplet excitons generated in a host are wasted, however when a phosphorescent compound is used to form an emissive layer, it has the advantage that an internal quantum efficiency reaches 100% since both of singlet excitons and triplet excitons are used (Baldo, et al., Nature, Vol.395, 151-154, 1998). Thus, an emissive layer formed of a phosphorescent compound has higher light emitting efficiency than that formed of a fluorescent compound.
Examples of the phosphorescent compound may include an organic complex compound complexed with a heavy metal such as Ir, Pt, Rh, and Pd. When a heavy metal is introduced into an organic molecule, triplet excitons and singlet excitons are mixed by a spin-orbital coupling generated by a heavy atom effect. Thus, transition which was originally prohibited can occur, and thus phosphorescence can effectively occur at room temperature. An example of the phosphorescent compound is disclosed in Korean Patent Publication No. 2004-0059304.
Various compounds using a transition metal compound including iridium, platinum, etc. as a high efficiency emissive material using phosphorescence have been reported. However, characteristics such as long lifetime and light emitting efficiency are not satisfactory for application in highly-efficient full color displays or low power consumption white light emission. Particularly, color purity and lifetime of blue light emitting materials need to be improved compared to green and red light emitting materials.